Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$246.91	5.379%	$260.1913	$260.19	$260.20	$260.20
Purchase #2	$32.36	8.203%	$35.0145	$35.01	$35.00	$35.00
Purchase #3	$196.69	12.514%	$221.3038	$221.30	$221.30	$221.30
Purchase #4	$137.61	4.241%	$143.446	$143.45	$143.45	$143.40
Purchase #5	$157.90	10.801%	$174.9548	$174.95	$174.95	$175.00
Purchase #6	$116.49	13.188%	$131.8527	$131.85	$131.85	$131.90
Purchase #7	$151.31	6.214%	$160.7124	$160.71	$160.70	$160.70
7 purchase totals =	$1,039.27		$1,127.4755	$1,127.46	$1,127.45	$1,127.50